As xerographic copiers and printers of all kinds increase in speed, it has become increasingly important to provide devices that can stack copy sheet output in a reliable manner. AS the output speed of these copy machines is increased, the first sheets to exit the paper path do not always have time to settle to the bottom of the stacking tray before succeeding sheets are forced into the trays by the transport systems of the machines. This often results in paper jams in the trays, and prevents the machine from operating properly.
The high rate of speed also causes stacking problems because force generated by the exit rolls sends each copy sheet so far up the stacking ramp that the following copy sheet runs into the trail edge of the previous copy sheet before that sheet has an opportunity to settle down the stacking ramp. Also, the trail edge of preceding copy sheets are sometimes lifted up and out of the stacking tray by the lead edges of incoming sheets because of a small interdocument sheet gap.
Each copy sheet must pass through the nip--a small gap that lies at the interface between the drive and idler rollers--as it exits the copy machine. Drive rollers are sometimes driven by motors which operate at varying speeds. For example, a Low Sheet Energy Uphill (LSEU) servo system operates at 1430 mm/s as the copy sheet enters the nip, and decelerates to 226 mm/s as the last 10 mm of the sheet passes between the rolls. The drop in speed allows the energy in the sheet to dissipate before the sheet exits the nip, thereby allowing the sheets to stack properly in the output tray. Once the copy sheet has exited the nip, the LSEU motor speeds up to receive the next incoming copy sheet.
In the example given, each sheet has a cycle time of 333 ms. That is, the sheet has 333 ms to move into the output tray after it enters the nip. Most of this time is used to accelerate and decelerate the motor. The current stacking method requires the motor to remain at a very low speed for an extended period of time, so that each of the preceding copy sheets can move away from the nip, and toward the bottom of the exit tray before the next sheet enters. The motor is accelerated in time to move the next sheet into the nip as the previous one moves toward the exit tray. If the motor accelerates too soon, the first sheet will not have had enough time to exit the nip, and the high speed acceleration profile will force the trailing edge of the sheet off of the rolls at a rapid pace, and cause the sheet to stack poorly. Thus, if the above method is used the advantage gained by increasing the maximum speed of a variable speed motor will be lost because the rollers will be forced to wait at the low speed while the exiting copy sheet moves out of the paper path.
There is a need, which the present invention addresses, for new apparatus which can rapidly move an exiting copy sheet away from the nip, such that a variable speed motor can accelerate and decelerate without having to wait an extended period of time before the next copy sheet can exit the paper path.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 5,029,743 to McNew discloses a system for passing long fan-folded documents and corresponding copy paper through a reproducing apparatus. It includes a collapsible, upright stand which carries a pair of copy paper roll supporting elements, a pair of paper guide plates pivotably and detachably connected to the top of the stand, and a guide bar for guiding copy paper from a roll on the stand to the guide plates.
U.S. Pat. No. 4,789,150 to Plain discloses a sheet stacking apparatus for use with throughput from high speed copiers or printers. It includes dual control flaps which act independently to provide positive control of sheets being stacked in the apparatus.
U.S. Pat. No. 4,627,718 to Wyer discloses a sheet curl control apparatus comprising a pair of co-acting rolls and baffle means positioned relative to said rolls so as to bend a sheet passing between the rolls about one of said rolls.
U.S. Ser. No. 08/583907 filed Jan. 11, 1996 by Jason P Rider et al. discloses an apparatus for corrugating copy sheets traveling at high rates of the speed toward an exit tray. The invention includes an idler shaft with idler rollers mounted upon it, and a drive shaft with drive rollers thereon. The drive shaft is positioned relative to the idler shaft such that one of the drive rollers is positioned between two of the idler rollers. The invention also provides means for applying different forces on the copy sheets passing between the idler rollers and the drive rollers.
U.S. Pat. No. 4,477,068 to Arter et al. discloses a document feeder for automatically inverting a duplexed original so that the second side may be copied. The inverting mechanism is a turnaround roll placed at the exit of the copy station, which cooperates with rollers located within the copy machine.
U.S. Pat. No. 4,407,597 to Kapp discloses a paper feeding apparatus which includes paper storage means for storing individual sheets of paper and feeding means for feeding a sheet of paper from the paper storage means in a paper feed direction along the paper feed path to the paper drive means. Guide means are provided having a first surface positioned along the paper feed path on the side opposite the paper storage means and extending parallel to the paper feed path to define a portion of the paper feed path. Means are also provided for defining a paper passageway between the second surface of the guide means and the paper feed path.
All of the references cited herein are incorporated by reference for their teachings.
Accordingly, although known apparatus and processes are suitable for their intended purposes, a need remains for an apparatus which can move an exiting copy sheet away from a nip, and enable a variable speed motor to operate at high speeds without having to wait for a previous copy sheet to clear the paper path before the next sheet can enter the nip.